An all-zero activation token row makes the dynamic per-row fp8 scale 0,
which turns the quantized data to NaN and the render to black frames on
torchao's plain-torch kernel path. The fused fbgemm/mslk quantize kernels
clamp zero rows internally, so the bug only reproduces on machines without
them, which is most user environments. Zero rows are real inputs, not a
corner case: Wan 2.2 zero-pads its text conditioning, and Hunyuan-1.5 and
Qwen-Image regenerate zero rows inside their transformer blocks every step.
Pass activation_value_lb=1e-12 to Float8DynamicActivationFloat8WeightConfig
whenever the installed torchao supports the kwarg (Float8Tensor rework,
0.13+), checked via inspect.signature so older torchao keeps exactly the
current behaviour; the existing Float8MMConfig fallback chain is unchanged.
Verified on GPU: with the forced plain-torch kernel path a zero-row input
NaNs without the floor and stays finite with it, and end to end on
HunyuanVideo-1.5 fp8 goes from a solid black frame (LPIPS 1.00) to a normal
render (LPIPS 0.225); on Wan the floor matches the condition_embedder
exclusion (LPIPS 0.211 vs 0.206). Same-seed renders with fused kernels
present are unaffected, and pre-quantized fp8 checkpoints stay valid since
weight scales are untouched.
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